A β-amino acid has been known as a compound that is useful as an intermediate for medicaments. In the past, in order to obtain a β-amino acid stereoselectively, there has been used a method for isolating and purifying a desired stereoisomer by optically resolving a racemic β-amino acid. However, according to this method, a theoretical yield is as low as 50% and this method becomes complicated due to multiple steps involved. So, the resulting β-amino acid becomes expensive as well. Accordingly, a method for producing a β-amino acid capable of realizing high efficiency and reducing the cost is expected to be developed.
In late years, it has been reported that there exists an amino acid aminomutase capable of catalyzing the reaction for synthesizing a β-amino acid using an L-amino acid which is relatively inexpensively available as a substrate.
For example, in Non-patent Document 1, there has been reported a method for synthesizing (R)-β-phenylalanine from L-phenylalanine using a phenylalanine aminomutase derived from Taxus caspidata. 
Meanwhile, in Non-patent Document 2, there has been reported a method for synthesizing β-tyrosine from L-tyrosine using a tyrosine aminomutase derived from Streptomyces globisporus. 
In addition, in Non-patent Document 3, it has been reported that β-phenylalanine is synthesized from L-phenylalanine using AdmH derived from Pantoea agglomerans strain Eh335.    Non-patent Document 1: Biochemistry, 46 (2007), pp. 9785-9794    Non-patent Document 2: Biochemistry, 42 (2003), pp. 12708-12718    Non-patent Document 3: Nature, 448 (2007), pp. 824-827    Non-patent Document 4: J. Am. Chem. Soc., 129 (2007), pp. 6988-6989